In some processes which are used in process gas technology, there is risk of gas explosions occurring. Measures therefore have to be taken in order physically to limit explosions in the industrial installations. Explosion protection apparatuses, such as fast-closing valves or slide valves, are used for this purpose, these being intended to prevent pressure waves and flames breaking through from a potentially explosive installation part into adjacent installation parts.
If an explosion occurs, it must first be identified. A closing command must then be issued and the closing process initiated and completed before the pressure wave and flame arrive at the relevant point.
Valves and slide valves are known having a compressed-air cylinder as drive and a compressed-gas reservoir having more than 10 bar overpressure in order to provide the closing energy. An explosive capsule valve and a compressed-air hose are arranged between the compressed-gas reservoir and the compressed-air cylinder. An incipient explosion is identified by a pressure sensor or an infrared sensor, and the explosive capsule valve is detonated electrically. This valve opens so that stored gas can flow from the compressed-gas reservoir via the compressed-air hose into the compressed-air cylinder, and closes the valve or the slide valve.
However, such valves and slide valves have the disadvantage that a relatively long time passes from the opening of the explosive capsule valve until the compressed-air piston is set in motion. In addition, the explosive capsule must be replaced whenever the compressed-gas reservoir is initiated. It is thus impossible to test these elements realistically.
Swiss Patent No. 685 134 discloses an explosion protection apparatus of the type mentioned initially, in which the compressed-air piston is a differential piston with a peripheral annular surface and an inner surface which is arranged concentrically with respect to said annular surface, whereas the peripheral annular surface and the inner surface can be acted on by a pressure generator and a compressed-gas reservoir. The pressure generator, which is initiated by the sensor, gives the differential piston a high initial acceleration which, once the inner surface has lifted off its contact surface, is further reinforced by the pressure from the pressure generator and the compressed-gas reservoir acting over the entire area of the differential piston.
This explosion apparatus admittedly allows short closing times to be achieved; however, it still has the disadvantage that the pressure generator is either a pyrotechnic element having a powder filling which can be detonated electrically or is a compressed-gas cartridge which releases the compressed gas by means of an explosive capsule which can be detonated electrically. Once again, it is thus impossible to test the pressure generator realistically.
Pyrotechnic detonators also have the major disadvantage that they are subject to weapon laws in some countries, which at least makes commercialisation more difficult. In addition, they require the wire from the sensor to the detonator to be protected against fracturing, in order to ensure reliable explosion protection.
DE-C1-43 16 584 discloses an apparatus for shutting off supply lines which are connected to building connections and are acted on by gases, which apparatus has a closing device which is arranged in a housing and is held in its open position by an initiation device in the basic state. The closing device is prestressed by means of a compression spring such that it is moved to its closed position once the initiation device has operated. The initiation device is operated by switching a solenoid valve, controlled by a control center, which is connected to the solenoid valve, as a function of signals which are obtained from gas detectors, smoke detectors, temperature sensors and/or a flow monitor.
In terms of the definition of its purpose, the shut-off apparatus is not an explosion protection apparatus and, in consequence, is also not aimed at achieving a closing time which is as short as possible in response to an explosion. In order to operate the initiation device, the solenoid valve must first build up a magnetic field, which takes at least about 50 ms. This is much too slow for an explosion protection apparatus.